Alignment interferometer telescope apparatus and method

ABSTRACT

An alignment interferometer telescope apparatus comprises a coherent laser source, a first beam splitter, a reference spherical mirror, a light source, first and second reticles, and a second beam splitter. At an interference location within the apparatus, a reference laser wave and a test laser wave are allowed to interfere to produce a combined laser wave.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/111,939, filed on Apr. 29, 2008, now U.S. Pat. No. 7,835,012which claims the benefit of priority under 35 U.S.C. §119 from U.S.Provisional Patent Application Ser. No. 60/924,124, entitled “AlignmentTelescope With Interferometer,” filed on May 1, 2007, both of which arehereby incorporated by reference in their entirety for all purposes.

FIELD

The present invention generally relates to telescopes and, inparticular, relates to alignment telescopes and interferometers.

BACKGROUND

Alignment telescopes are integral to most, if not all, optical sciencesdepartments, equipment manufacturers, and optical integration houses.Typically alignment telescopes are a refractive type. Two lenses aredisplaced from one another within an optical path to focus on anobserved image. Thus they can align objects along a common axis. Inaddition, some types of alignment telescopes have auto collimationfeatures built into them. This feature allows them to measure angularerror of reflective objects along the line of sight of the telescope.

SUMMARY

In accordance with one embodiment of the present invention, an alignmentinterferometer telescope (“AIT”) is provided that merges an alignmenttelescope with a large unequal path interferometer. This combinedinstrument improves the fidelity of the alignment telescope'smeasurement capabilities. The design is based on a standard alignmenttelescope, so as to make the alignment interferometer telescopeinterchangeable with existing mounting hardware.

In accordance with one aspect of the present invention, an alignmentinterferometer telescope apparatus comprises a coherent laser source, afirst beam splitter, a reference spherical mirror, a light source, firstand second reticles, and a second beam splitter. The coherent lasersource is configured to produce a coherent laser wave. The first beamsplitter is configured to receive the coherent laser wave and to splitthe coherent laser wave into a reference path laser wave and into a testpath laser wave. The test path laser wave is to be transmitted to anobject outside the alignment telescope interferometer apparatus and tobe returned to an interference location within the alignmentinterferometer telescope apparatus upon reflection from the object.

According to an aspect of the present invention, the reference sphericalmirror is configured to receive the reference path laser wave and toreflect the reference path laser wave to the interference location. Thelight source is configured to produce a light. The first reticle isconfigured to receive the light and to project a projected image. Thesecond reticle comprises a reference image. The second reticle isconfigured to receive the projected image and to superimpose theprojected image with the reference image. The second beam splitter isconfigured to receive the projected image as a first beam. The firstbeam is to be transmitted to the object, to be returned to the secondreticle upon reflection from the object, and to be superimposed with thereference image. The interference location is configured to combine thereference path laser wave and the test path laser wave to produce acombined laser wave.

According to another aspect of the present invention, a method for atelescope is provided. The method comprises producing a coherent laserwave, splitting the coherent laser wave into a reference path laser waveand into a test path laser wave, transmitting the test path laser waveto an object outside the telescope, receiving the test path laser waveat an interference location within the telescope upon reflection fromthe object, reflecting the reference path laser wave to the interferencelocation, and combining the reference path laser wave and the test pathlaser wave to produce a combined laser wave.

According to an aspect of the invention, the method for a telescope alsocomprises producing a light, projecting an image from a first reticlewith the light, transmitting the projected image to the object,receiving the projected image at a second reticle, and superimposing theprojected image with a reference image from the second reticle.

Additional features and advantages of the invention will be set forth inthe description below, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

It may be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

In the following description, reference is made to the accompanyingattachment that forms a part thereof, and in which are shown by way ofillustration specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand changes may be made without departing from the scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is an illustration of an exemplary alignment interferometertelescope apparatus in accordance with an embodiment of the invention;

FIG. 2 is a block diagram of an exemplary alignment interferometertelescope apparatus in accordance with an embodiment of the invention;

FIG. 3 illustrates an exemplary alignment interferometer telescope as alab setup in accordance with an embodiment of the invention;

FIG. 4 illustrates exemplary components for an exemplary alignmentinterferometer telescope apparatus in accordance with an embodiment ofthe invention;

FIG. 5 is a picture of exemplary components for an alignmentinterferometer telescope apparatus in accordance with an embodiment ofthe invention;

FIG. 6 illustrates reticle patterns in accordance with an exemplaryembodiment of the present invention;

FIG. 7 is a graph of results obtained using an exemplary embodiment ofthe present invention;

FIG. 8 illustrates exemplary pupil image optics in accordance withaspects of an exemplary embodiment of the present invention;

FIG. 9 illustrates exemplary beam splitter and reference sphericalmirror optics in accordance with aspects of exemplary embodiments of thepresent invention;

FIG. 10 illustrates interferometry fringes taken using an exemplaryembodiment of the present invention;

FIG. 11 is a graph of fringe visibility obtained using an exemplaryembodiment of the present invention;

FIG. 12 is a graph of fringe visibility obtained using an exemplaryembodiment of the present invention;

FIG. 13 illustrates fringe visibility obtained using an exemplaryembodiment of the present invention;

FIG. 14 illustrates fringe visibility obtained using an exemplaryembodiment of the present invention; and

FIG. 15 illustrates fringe visibility obtained using an exemplaryembodiment of the present invention and an aspect of some of theequipment used in an embodiment of the present invention to acquire thepictures of fringe visibility.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth to provide a full understanding of the present invention. It willbe apparent, however, to one of ordinary skill in the art that thepresent invention may be practiced without some of these specificdetails. In other instances, well-known structures and techniques havenot been shown in detail to avoid unwarranted obscurement of the presentinvention.

FIG. 1 illustrates an alignment interferometer telescope in accordancewith an exemplary embodiment of the invention. Alignment interferometertelescope 5 may include laser source 10 to provide laser wave 15 to afirst beam splitter 20. Laser source 10 may be any conventional lasergenerator such as a Helium-Neon laser generator, or a solid state laser.One of skill in the art would understand that laser wave 15, being usedfor interferometry, is preferably coherent. That is, the laser generator10 produces a laser beam with a constant (or fairly constant) sine wavewith a known amplitude and frequency.

Laser wave 15 is directed at beam splitter 20. In beam splitter 20 thelaser wave 15 is split into two laser waves: a reference laser wave anda test laser wave. The reference laser wave is transmitted from beamsplitter 20 to reference spherical mirror 30. (Reference sphericalmirror 30 is also shown in FIG. 9 as element 910; further in thatfigure, the first beam splitter is shown as element 900, the second beamsplitter is shown as element 920, and the optical/laser waves are shownentering element 900, and being reflected back to element 900 by mirror910.) Upon reaching reference spherical mirror 30 the reference laserwave is reflected back to beam splitter 20, where it is redirected. Theredirection of the reference laser wave at the first beam splitter 20 isdiscussed in further detail below following discussion of the test laserwave.

After splitting laser beam 15 the first beam splitter 20 transmits thetest laser wave out through secondary lens 90 and objective lens 80.Objective lens 80 and secondary lens 90 may be conventional lensessuitable for telescopic observation. Lenses 80 and 90 are discussed ingreater detail herein. The test laser wave continues in an outwarddirection from the alignment interferometer telescope until it strikesan object along the observation axis of the telescope. This object maybe any number of things that are located outside alignmentinterferometer telescope 5, for example, a flat, a sphere, a lens, oranother object that may be observed with an alignment telescope (theobserved object is not illustrated in the figure).

Upon striking the object being observed the test laser wave isretro-reflected back to the telescope, where it travels back throughobjective lens 80 and secondary lens 90, to re-enter the first beamsplitter 20. At a point within first beam splitter 20 the test laserwave and the reference laser wave intermingle. The point where theyfirst mingle is approximately at the hypotenuse of a triangle created bypicturing that the beam splitter is made of up two equal triangles asshown in FIG. 1. As used herein, intermingling describes theinterference location, or the presence of each of the reference laserwave and the test laser wave in the same optical path at the same time.Interference may describe the interaction of the two waves, forinstance, combining, beating, joining, merging, coalescing, or othersimilar actions. The two laser waves may be permitted to interminglefrom about the hypotenuse of the first beam splitter 20 along an opticalpath to about the notch splitter 110.

Because the test laser wave and the reference laser wave traveldifferent paths to reach the interference location, the individual sinewave of the reference laser wave in all likelihood is at least somewhatout-of-phase with the individual sine wave of the test laser wave. Ifthe two sine waves are found to be perfectly in-sync at the interferencelocation, then the two waves are combined to produce a combined wavewith the greatest-possible amplitude. If the two sine waves are found tobe perfectly out-of-sync at the interference location, then the twowaves are combined to produce a flat wave, that is, a sine wave withoutany positive or negative amplitude or a “flat line.” In most instances,however, the combined wave is somewhere between perfectly in-phase andperfectly out-of-phase.

The differences between the reference laser wave and the test laser wavemay also be described as possessing constructive elements and/ordestructive elements. That is, at the interference location, positiveamplitudes of either sine wave are considered to be constructive, whilenegative amplitudes of either sine wave are considered to bedestructive. Additional aspects of interference are described in greaterdetail herein.

The combined laser wave is permitted to travel along an optical path toreach notch splitter 110. Notch splitter 110 prevents harmful aspects ofthe laser light (e.g., the reference laser wave, the test laser wave, orthe combined laser wave) from being sent to the eyepiece 120 to preventpossible injury to an observer. Eyepiece 120 may be a typicalobservation eyepiece fashioned for human comfort and/or it may include acamera mount and/or a charged coupled discharge device for taking photosincluding potentially digital photos.

At notch splitter 110 the laser wave is allowed to travel to pupilimaging module 130, where module 130 analyzes each of the sine wavesfrom the reference laser wave, the test laser wave, and the combinedlaser wave. Through this analysis the pupil imaging module 130 producesa first pupil image that may be based upon the sine waves of thereference laser wave and/or the combined laser wave. It also produces asecond pupil image that may be based upon the sine waves of the testlaser wave and/or the combined laser wave. In additional exemplaryembodiments the pupil images may be based upon the sine waves of atleast one of the reference laser wave, the test laser wave and thecombined laser wave. Alignment of the pupil images occurs automaticallywhen the projected reticle 50 is centered within the reference reticle70, as is explained in greater detail herein.

The analysis performed at pupil imaging section 130 may be done with aprocessor, a computer, with software, and/or with an algorithm. Further,the pupil imaging module 130 may include selectively adjustablecomponents (including manually and/or automatically selectivelyadjustable components) for alignment/adjustment of the first and secondpupil images. Selectively adjustable components may include, forexample, mirrors, lenses, prisms, wedges, and/or windows. In variousexemplary embodiments of the present invention, when the telescopeapparatus is out-of-alignment, the first and second pupil images may beshown to not overlap or to only partially overlap, and when thetelescope apparatus is properly aligned, the first and second pupilimages may be shown to overlap or to substantially overlap.

The first and second pupil images are projected to a viewing plane 140where the first and second pupil images may be observed for purposes ofboth alignment of the telescope and for intensity/brightness. If theindividual waves of the reference laser wave and the test laser wave aremostly in-phase, the first and second pupil images approach a state ofgreatest overall intensity/brightness. When the individual waves of thereference laser wave and the test laser wave are mostly out-of-phase,the first and second pupil images approach a state of lesser overallintensity/brightness. The varying degrees of intensity/brightness of thefirst and second pupil images may be compared, as one skilled in the artwould understand, by overlapping the pupils on a viewing plane and thennoting the differences between produced fringes.

An example of fringes produced by an exemplary embodiment of the presentinvention is shown in FIG. 10. Pupil images 1000 are projected to aviewing plane. The pupil images 1000 are displayed at the viewing plane,for example, the interferometer pupil image plane 140 shown in FIG. 1.The pupil images may be otherwise displayed for observation; forexample, the pupil images may be displayed on a display monitor, or avideo screen, or captured by a charged coupled discharge device, and/orthey may be supplied to an eyepiece such as the eyepiece shown inFIG. 1. Once displayed the pupil images 1000 are observed fordifferences in the fringes 1010, or those sections of the pupil images1000 shown by the alternating black and white stripes.

Once again referencing FIG. 1, light source 40 produces a light 45 thatis transmitted through first reticle 50. When light 45 travels throughfirst reticle 50 a projected image is produced, for instance the image600 shown in FIG. 6. The light with the projected image is hereaftermostly referred to as a first beam. The first beam continues past firstreticle 50 and into a second beam splitter 60. At beam splitter 60 thefirst beam is further transmitted out of the telescope apparatus throughsecondary lens 90 and objective lens 80.

The first beam then reflects from the previously discussed observedobject that is external to the telescope apparatus and returns in aretro-reflection first through objective lens 80, then through secondarylens 90, back through the first and second beam splitters to arrive at asecond reticle 70. Second reticle 70 is a focus/reference reticle andincludes a reference image such as that shown in FIG. 6 as element 610.

In an additional exemplary embodiment of the present invention, thereticles 50, 70 may be selectively adjustable. For instance, at leastone of the reticles 50, 70 may be selectably adjustable (or movable) toallow for displacement measurements. To implement an adjustable reticle,the focus position of the reticle is placed off of the beam splitters20, 60 to allow access for a mechanical mounting. Two reticles are usedat the location of reticle 70, one in each axis so that X & Ydisplacements can be measured independently. Micrometer adjustmentmechanisms with their actuator knobs located outside the housingdirectly move the reticle to a desired position. Numbers on themicrometer provide offset. Unit magnification over all of focalpositions and/or a mechanical compensator is required to translate thepositional value to an object displacement, as one of skill in the artwould comprehend. The reticles may also be automatically selectivelyadjustable; for instance, a computer may control the aforementionedthrough software, by a processor, and/or by an algorithm, as one ofskill in the arm would comprehend.

Returning to FIG. 6, at second reticle 70 the projected image 600 fromthe first beam and the reference image 610 are superimposed to createimage 620. If the optics of the telescope apparatus are properly alignedthen the superimposed image 620 may be viewed through the eyepiece 120with the crosshairs of the reference image 610 centered on thecenter-most concentric circle of the projected image 600. One ofordinary skill in the art would understand that at least one of thereticles 50 and/or 70, and/or their associated optics, and/or lens 80and/or 90, may be fashioned so as to be selectively adjustable so as toalign the superimposed image 620 in view of an object being observed.

Further as shown in FIG. 1, relay module 100 relays the previouslydiscussed optical paths (to include the observation path and the laserinterference path) to and from the second reticle 70 and the notch beamsplitter 110. The relay module 100 is discussed in greater detailherein. One of ordinary skill in the art would comprehend various waysin which the relay system may be implemented.

FIG. 2 is a block diagram that illustrates a modular view of anexemplary embodiment of the present invention. An alignmentinterferometer telescope 201 includes an alignment telescope objectivearrangement and beam splitter module 200, an interference reference pathand beam splitter module 210, a relay and beam splitter module 220, aneyepiece module 230, and a pupil imaging module 240. These exemplarymodules of the present invention are discussed in greater detail below.

An exemplary manner of making an embodiment of the present inventionincluding the alignment telescope objective arrangement and beamsplitter module uses a two-lens system as a basis for the overallobjective system. Referring to FIG. 1, an outer, fixed objective lens 80is used along with an inner, movable secondary lens 90. Each lens 80 and90 consists of an air spaced achromat. The air spacing is to reduceghosting due to a cemented lens interface especially when a laser isbeing used, such as the laser wave 15. For closest focus, the lenses 80and 90 may be relatively close to each other, for instance with aseparation of about 25 mm in mechanical mounting. At infinity focus thelenses 80 and 90 would be at their maximum separation, for example aboutthe referenced 25 mm. Focusing between near-focus and infinity-focus isachieved by varying the secondary lens within the distance separatinglenses 80 and 90. A simplified approach to understand the focusingtechnique is, at near focus, the secondary lens 90 collimates thereticle 70 and the objective lens 80 focuses the collimated light 45.

For infinity focus, the secondary lens 90 is closer to the reticle 70and thus has little effect on the optical system. Hence the reticle 70is at the focus of the objective lens 80, producing collimated light.The beam splitters 20 and 60 may be a cube design to minimizeaberration, for ease of manufacturing, and for ease of mounting inside abarrel housing (not shown), and also to create perpendicular (or otherknown) surfaces to align the reticles 50 and 70 against. For example, inan exemplary embodiment of the present invention, one surface of a cubedesign beam splitter 60 may be used to mount the projection reticle 50and another, perpendicular surface may be used to mount the referencereticle 70.

Materials for the transmission portions of the reticles 50 and 70 may bethe same as the materials used for the transmission portions of the beamsplitters 20 and 60 to minimize ghosting. A crosshair may be used forthe reference reticle 70 and an illuminated ring pattern for theprojected reticle 50, as shown in FIG. 6. Further as shown in FIG. 6,the projected image 600 includes multiple rings that may be equal toabout one arc minute with a range of 30 arc minutes. The outer surfaceof the objective lens 80 is defined as the clear aperture (as the term“clear aperture” would be known to one of ordinary skill in the art),since this is the restricting optical surface.

The interferometer reference path & beam splitter module shown in FIG. 2includes (as shown in FIG. 1) a laser source 10 for the laser wave 15.An exemplary embodiment of the present invention includes use of asingle mode fiber (SMF) for about 633 nm. The cube beam splitter 20splits the laser beam between reference and test laser waves. Thereference laser wave transmits un-deviated through the beam splitter 20while the test laser wave is reflected and transmitted through lenses 90and 80 in a trajectory vector away from the telescope apparatus. Thebeam splitter 20 may be attached to the alignment telescope beamsplitter 60. To reduce ghost reflection, both beam splitters 20 and 60may be made of the same transmission material and may be optically incontact with one another. A good anti-reflective (AR) coating optimizedat 633 nm may be used on the outer surfaces where the reticles 50 and 70are not attached (since the reticles 50 and 70 are at the focus,coatings may induce surface defects that may result in poor imagequality).

In an exemplary embodiment of the present invention, the retro reflectormirror 30 may be a coated spherical surface and be oversized to allowfor easy alignment and to induce tilt fringes. An f-number slightlyfaster than the objective system shall be used to facilitate ease ofalignment. Typical SMF output is F/5 which requires a light stop tomatch the objective system, and to reduce stray light. Design conceptsinclude a complete path that goes through both beam splitters 20 and 60.Design concepts should perform over a 633 nm wavelength. An interferencelocation includes at least a portion of beam splitters 20 and 60, andinterference takes place where the two beams, i.e., the reference andtest laser waves, each coincide in the same optical path at the sametime. A portion of this interference location includes the generallocation of the hypotenuse of beams splitter 20 and most of the opticalpath of beam splitter 60.

FIG. 2 also displays the relay system & beam splitter module, and thefollowing description provides an exemplary manner of making this moduleas an embodiment of the present invention. The relay system 100 is shownin FIG. 1, and allows image access to both the eyepiece 120 and thepupil imaging system 130. Magnification may be on the order of 1× toallow the eye to resolve 5 arc seconds to null the alignment telescopereticles. WFE may be in single pass since at least some exemplaryembodiments of the present invention only use single pass.

In exemplary embodiments of the present invention, pupil size may beapproximately 4 mm in diameter to allow 1:1 imaging onto a camera (notshown) using the pupil imaging system. In various embodiments, the beamsplitters 20 and 60 are a cube design to facilitate mounting and reduceaberrations. A notch filter 110 is incorporated in the beam splitter tolimit and/or prevent the amount of laser light reaching an observer'seye as a laser safety requirement. The focal point (not shown) is beyondthe beam splitters 20, 60 in reference to the relay system 100 to reducebeam splitter surface quality effects on the image.

FIG. 2 also includes a pupil imaging module. In exemplary embodiments ofthe present invention, the pupil imaging module includes a camera, andimages the pupil images (otherwise known as interferograms) over theentire focusing range onto a charged coupling device (CCD) imagingsurface (such as a digital camera). CCD camera size may be 768×494pixels with pixel pitch of 8.4×9.8 microns, for example, or other knownvalues for a standard CCD camera. Pupil imaging size may be 4 mm indiameter to fill the CCD image surface over the entire focusing range.Pupil lenses should be located at least 20 mm from the CCD imagingsurface and at least 5 mm from the beam splitter 60 for mechanicalmounting for preferred pupil imaging. Operational concepts includehaving a two-element air space lens system to collimate the pupil imageand another two-element air space lens system to image the pupilimage(s) onto the CCD.

FIGS. 1 and 2 also include an eyepiece or an eyepiece module. Theeyepiece 120 may be a commercial off the shelf design with a minimum of12.5 mm of eye relief to accommodate persons who wear eyeglasses, andshould image at least ±1 degree. Its requirements may be based on themagnification required to view better than the 5 arc seconds of arelayed image.

In determining the optical design process, optical element startingpoints were laid out based on first order design principles using thefollowing equations. In the below equations, each doublet is simplifiedinto a singlet and paraxial equations are used. The below equations maybe used to determine the powers of the lenses 80 and 90. These state thefollowing equations to derive their corresponding components/quantities:

Objective  Lens  Optical  Power$\Phi_{A} = \frac{\left( {{ms} - {md} - s^{\prime}} \right)}{msd}$

Secondary  Lens  Optical  Power$\Phi_{B} = \frac{\left( {d - {ms} + s^{\prime}} \right)}{{ds}^{\prime}}$F/#=f/CA  F-Number

Magnification $m = \frac{s^{\prime}}{s}$

s—Object to objective lens (principal plane)

s′—Secondary lens (principal plane) to image plane

d—Distance between objective and secondary lenses (principal planes)

f—Effective focal length

CA—Clear aperture

All values are positive except for s, which is negative. Based on theoverall length of the telescope and the magnifications needed for themodules stated in the block diagram of FIG. 2, each module's optics,element power, and locations may be calculated. (Note that these valuesare starting points for exemplary embodiments of the present invention,and are not meant to necessarily be final design values.) For theobjective lens system (ignoring the beam splitters 20, 60) and using thenear focus of 400 mm for s, 200 mm for d, 100 mm for s′ and 35 mm forthe CA. Inserting these values into equations 1-4, the power for thelenses are:Φ_(objective)=0.0025 1/mm (f_(A)=400 mm)Φ_(secondary)=0.0100 1/mm (f_(B)=100 mm)

For the relay system 100 based on the allocated thickness and 1:1magnification, a two lens achromatic system may be used. The first lenscollimates the objective system image point while the second onere-focuses it. The standard rule of thumb for a glass plate in focusingspace, to simulate the beam splitter 20, 60, is to extend the focallength by approximately ⅓ the thickness of the glass, based on an indexof 1.5. A 25.4 mm cube beam splitter 20, 60 yields a focal shift of 8.47mm. Using a separation of 12.7 mm, relay track length of 120 mm, 8.47 mmdue to the beam splitter 20, 60 and the required magnification, thefocal length of the two lenses are equal. The focal length for the twolenses may be calculated to be:f _(A)=120−8.47−12.7−(f _(A))f_(A)=49 mmf_(B)=49 mm

For the pupil imaging system 130, two lenses 132 and 134 image theinterferogram (pupil images) onto a plane 140, whether that plane is aviewing plane, a CCD camera, or other image representation forobservation. In an exemplary embodiment of the present invention, afterimaging through the relay system 100 and beam splitter 20, 60, the pupilimage would be located approximately 15 mm from the beam splitter 20,60. To image the pupil image/interferogram a further distance from thebeam splitter 20, 60 (that is, to reach the CCD camera), a relay system(such as relay system 100) is used. Using a track length of 100 mmincluding the beam splitter 20, 60 and pupil location, 8.47 mm for thebeam splitter 20, 60, 12.7 mm separation and 1:1 magnification, thefocal length of the two lenses 132 and 134 are equal. The two lenses aretherefore calculated to be:2(f _(A))=100−8.47−12.7f_(A)=f_(B)=39 mm

The design process begins with the objective system comprising lenses 80and 90. Subsequent sections are added later on so that the combinedsystem's performance can be verified as each step is completed. To startthe objective system, a search of known lens design was performed. Anideal starting lens was found in Warren Smith's “Modern Lens Design aReference Manual” (McGraw-Hill, Inc. San Francisco, Calif., 1992. p 66).The lens is a Fraunhofer cemented achromatic objective made from commonand easy to manufacture materials with the following specifications:

F/# 7

Half FOV—1 degree

Effective Focal Length (EFL)—99.98 mm

CA—14.4 mm

Material—BK7 and SF1

A single pass system was modeled with the object set for infinity, fieldset to 0, 0.7 and 1 degree, and the wavelengths set to visible (486.13,656.27, 587.56 nm) and Helium Neon (HeNe 632.8 nm). The visiblewavelengths were equally weighted along with the HeNe. An on-axis fieldwas weighted 10 times higher than the other fields since theinterferometer works mainly on-axis and requires good performance. Firstthe lens 90 was scaled to have the required 35 mm clear aperture. Thenit was duplicated and inserted behind the first objective lens 80 as thesecondary lens (90). The beam splitter 20, 60 was then added to themodel with its back surface as the focus surface. Its total thickness of50.8 mm incorporated both the alignment telescope and the interferometerbeam splitters 20, 60. Variables were all the Radius of Curvatures(RoC).

The lens separations were set as in the first order design with anobject at infinity. At this time the optimization was used to find asolution for this setup. Optimization figure of merit was based on theRMS wavefront over all wavelengths and fields. To fine tune thesolution, the cement surfaces are replaced with a fixed separation of 1mm and both de-cemented RoC were allowed to vary. When the performancewas diffraction limited, configurations were added to allow optimizationover the focusing range. Six different ranges were used, infinity,10,000, 5,000, 1,000, 500 and 400 mm.

Pickup and thickness limits were used to control the travel range of thesecondary lens 90. This technique allows for mechanical mountingdistance between the objective lenses 80, 90 and the beam splitters 20,60. New operands were created to incorporate the configurations formerit function. Optimization was quick and resulted in an objectivesystem having a worst-case WFE of 0.3 λRMS over all the tested ranges,tested configurations, and tested wavelengths.

In an exemplary manner of making an embodiment of the present invention,the interferometer reference path and beam splitters 20, 60 may be addedto the optical model after the objective module. Not that theinterferometer path shares the same optical path as the alignmenttelescope's beam splitters 20, 60 and focal point. Since the referencepath is the reference for the interferometer, it needs to be better thanthe test path. A performance factor of 4 was chosen between thereference and test paths.

Given that an exemplary embodiment of the present invention utilized amonochromatic interferometer, only a HeNe wavelength was required. Thecalculated performance for the reference beam was 0.05 λPV at 633 nm. Toslightly overfill the pupil size of the test laser wave an F/6.0 beamwas used. Design accommodations took into account mounting and alignmentof the SMF fiber (for example, the fiber 430 shown in FIG. 4, and asshown being aligned in FIG. 5) and reference spherical mirror 30. TheSMF fiber (for instance, the fiber shown as element 430 in FIG. 4) wasmounted in the range of 12.7 mm from the first surface of the beamsplitter 20, 60 as shown in FIG. 5. In FIG. 5, the SMF fiber output 500is shown emitting to the surface of the beam splitter 20, with thereflected reference laser wave (retro-return image) shown as element510. The air space between the fiber output 500 and the beam splitter 20allowed room for light baffles to reduce stray light emanating from theSMF fiber and for mechanical adjustments. 20 mm of air spacing wasallocated for the reference spherical mirror 30 (shown in FIG. 1) toaccommodate mechanical mounting and adjustments. To minimizemanufacturing costs, a spherical surface for the mirror 30 was utilized.

A single pass system was modeled with the fiber 500 (shown in FIG. 5)set at 12.7 mm from the first beam splitter 20, field set to 0, 0.35 and0.5 degree, and the wavelengths set to HeNe (632.8 nm). On-axis fieldwas weighted 10 times higher than the other fields since theinterferometer reference path works on-axis. The F/6.0 beam was setusing a dummy surface after the fiber set to a thickness of 6 mm and aCA of 1. A negative thickness pickup on the next surface returned thebeam to the source.

The previous is a standard modeling technique that allows control of thef-number without interfering with the system's setup and reducesoptimization complexity. The RoC for the reference spherical mirror 30(shown in FIG. 1) was estimated at the distance from the SMF fiber tothe retro return path to be 60 mm concave. Viewing the model layout thenallowed for refining the reference spherical mirror 30 by manuallyadjusting it until it looked that the focus of the reference sphericalmirror 30 was at the surface of beam splitter 20.

Variables included the retro reflector RoC and the separations of theretro sphere and SMF fiber to the beam splitter 20. Constraints wereplaced on the thicknesses to control their range. The material for thebeam splitters 20, 60 was identical to the materials used for theobjective system. Figure of merit was based on the RMS wavefront overall fields. Optimization was quick and resulted in the interferometerreference system having a worst-case on-axis WFE of 0.0545λ PV over theentire field. The performance goal was ≦0.05λ peak-to-valley (PV). Inorder to improve the performance, a conic constant or an increase inf-number would be required. To minimize manufacturing cost andcomplexity, the as-designed performance is acceptable. If theperformance is rounded (0.05λ) it meets self-imposed performance goals.

Referring to FIG. 10 shows that an imaged pupil interferogram (or twopupil images contrasted with one another). Note that the scale factor inthe figure has the fringe/wave value set to one. Since the exemplaryembodiment of the present invention utilized a single pass system theretro beam does not return to the same starting point.

The below table shows requirements for an exemplary embodiment of areference spherical mirror used as part of the present invention (suchas element 30 shown in FIG. 1). While the table shows variousrequirements, the stated requirements apply only in the strictest senseto the example given. One skilled in the art would comprehend that otherreference spherical mirrors could be utilized in different embodimentsof the present invention, and that these other reference sphericalmirrors may utilize at least some varied requirements along with some ofthe requirements listed in the below table.

Reference Spherical Mirror Requirements For An Exemplary Embodiment ofthe Present Invention Verification Method Requirement Requirement UnitsDesign Units Optical System [Alignment Telescope & Interferometer] NearFocus in Front of Objective Lens 406.4 mm 400 mm Far Focus in Front ofObjective Lens infinity NA Infinity NA Clear Aperture at Objective Lens≧35 mm 35 mm No Ghosting the Interferes with the Yes NA x System'sPerformance Alignment Telescope WFE (single pass from object to eyepieceλ/3 RMS (λ = all wavelengths) nm 0.12 waves over field) F/# (throughfocusing range) 5-8 NA 7 NA Path 1: Object to Eyepiece Yes NA x Path 2:Projected Reticle to Retro Surface Yes NA x to Eyepiece SpectralBandwidth 500-650 nm 486-656 nm Adapter for Color Filter Yes NA x FullField of View ≧1 Degree x x Null <5 arc seconds Interferometer WFE(reference to test path) ≦λ/5 PV (λ = 633 nm) nm 0.05 waves SpectralBandwidth 633 nm 633 nm Path 1: Source to Reference Retro Yes NA yes NASphere to Camera Path 2: Source to Retro Surface to Yes NA x CameraFringe Visibility for 4 - 100% Reflection 0.25 NA x Full Field of View0.001 Degree 0.001 degrees

The relay system and beam splitter module shown in FIG. 2 is the nextmodule to be integrated into an exemplary manner of making an embodimentof the present invention. A search for a known lens to fit the firstorder design was previously performed. Since the objective lens 80, 90described above worked well as an imager for an infinite object, asimilar lens was used for the relay system. The same materials and stepsused above in relation to the objective lenses 80, 90 were re-utilizedfor relay system 100 lenses. Re-using the same materials and stepsallows for quality of optical paths, and also helps to controlmanufacturing costs.

Each lens for the relay system 100 (shown in FIG. 1) was separatelyoptimized for their respective focal length (f=49 mm) as defined in thefirst order design. The general requirements (FOV and wavelengths) wereidentical to that for the objective system except the weighting for theHeNe wavelength was made equal with the other wavelengths. Becauseinterference happens at the hypotenuse of the interferometer beamsplitter 20, the relay system 100 is common to both beams and does notrequire high precision. Variables were all of the RoC and thethicknesses. The operands that made up the figure of merit were the RMSwavefront for all fields and wavelengths.

After these separate lenses were optimized, they were integrated ontothe end of the objective system model, with their positive lenses facingeach other. The air separations keep to the first order design values.Additionally, a reticle glass plate was attached to the objective systembeam splitter 60 along with a beam splitter 20 near the relayed focus.The beam splitter 60 splits the beam between the eyepiece and theinterferometer camera that is a part of pupil imaging module 130. Onlythe through-path of the relay beam splitter was modeled. It was notnecessary to model the reflected path separately since the amount ofglass that both paths see is the same, only a parity changes.

The hypotenuse of beam splitter 60 is important for alignmentrequirements since the reflected beam undertakes a two times angularerror deviation. A separation of at least 5 mm was used between the beamsplitter 60 and focus relayed by relay module 100. The reason for thisspacing is to eliminate cost and manufacturing complexity to the beamsplitter 60. When a beam focuses on an optical surface, the surfacequality (scratch/dig) of that surface is required to be very tight (10/5or better) to eliminate blotches in the image.

With the Depth of Focus (DOF) for the F/7 beam, worst-case, at 0.064 mm(5),DOF=2λF/# ²DOF=0.064 mm

the separation is over 77 times that of the Raleigh λ/4 DOF range.Surface quality for the two surfaces on the beam splitter that are usedcan now be loosened. For the reticle 70, a standard plate size wasmodeled, 0.062 inch thick made from fused silica. The beam splitter 60was also made from fused silica since it is a good material forfabrication and handling. Variables were all of the RoC and thicknesses.Constraints were used in the operands to limit the motion of thevariable. These were the allowed total track length of 120 mm,magnification of 1:1, pupil size and location and beam splitter 60distance to relay focus of approximately 5 mm.

With the setup complete, the optimization was turned on and based on theRMS wavefront over all fields and wavelengths. Optimization for thisblock required manual guidance to prevent the system from getting caughtin local minima or creating an unobtainable design. The optimizationtechnique was similar to the objective system. First the cementeddoublets were optimized, then the cement was removed and the twode-cemented surfaces were allowed to vary. Next the thicknesses and airspacing were allowed to vary.

Several final designs were evaluated for performance andmanufacture-ability. These designs included two-, three-, andfour-element designs. A quick trade study showed best performance andmanufacturability was the four-element design. One of the parameters inthe trade study was the location of the exit pupil over all of the focuspositions at the HeNe wavelength. This is the location that the pupilimaging system 130 images onto the CCD camera at plane 140. Largevariations in position result in the pupil imaging system 130 lensesworking harder and thus having tighter tolerances. With the 4-elementdesign the pupil location varies by less than 0.0001 mm, and it has adiameter of 6 mm which almost fits the CCD camera requirement of 4 mm.

The performance of the relay system described above has a worst-case WFEof 0.256λ RMS over all tested configurations, tested fields and testedwavelengths. A feature of an embodiment of the present inventionincluded the relay system 100 flipping the viewed object upside down.The next optical modules, the eyepiece and pupil imaging modules, flipthe image once more so that a viewer views an upright image.

During testing of an embodiment of the present invention, it wasdiscovered that performance was improved when the overall track lengthof the alignment interferometer telescope apparatus was grown to 132 mm,which is 12 mm longer than an initially derived error budget of 120 μm,Although this directly affects the overall length of the apparatus, theperformance increase was found to be substantial. For instance,magnification comes in at 1.25:1, which is close to the 1:1 ratiorequired by an initial error budget. The resulting image size is 5.26 mmin radius with a pupil radius size of 3.0 to 3.2 mm over all focalpositions. For the pupil imaging system the magnification is almost 1:1so the optical design remains straightforward.

The pupil imaging system with camera is the final module to be includedinto an exemplary manner of making an embodiment of the presentinvention. As with the relay block 100, the pupil imaging system 130 isactually a relay system, except it images the pupil images onto a plane140 to be viewed by a camera or other device. The intermediate pupilimage lies 30 mm before the relay beam splitter 60 as measured from therelay system 100. Using the same lens starting point as with the lastsections (as described above in relation to the relay system and beamsplitter module), the cemented lens 132, 134 is incorporated into themodel. The lens 132, 134 design was initially optimized for the focallength (f₁=39 mm) as determine in the derived requirements. In thisprocess, the cemented interface was removed as before. Then the lenses132, 134 were inserted into the model and duplicated to produce thetypical two-lens relay system as stated above.

Control of the optimization was different since the camera was imagingthe pupil at plane 140, and not the focused image. A single real-raytrace at the y axis limit was used to control the pupil image size ineach configuration, since the system is rotationally symmetric. Thelocation of the pupil was established using a fixed distance (25 mm)from the last lens to the camera and a total track control of 53 mm.This allowed for mechanical mounting and imaging onto the CCD where theCCD sits inside of a camera body.

To solve for the actual pupil location, a pupil solve was used on thecamera pupil imaging surface 140. After the solve, an ideal lens wasinserted to focus the system. Optical programs prefer to have a focusedpoint at the end of the model. They optimize better, are less prone touncontrolled optimization and most of their analysis tools are based onfocal systems. For each configuration, operands set the targeted pupilsolve thickness to zero. The focal length for the ideal lens was allowedto vary since its location was only needed for optimization purposes.Afterwards, this lens can be removed or ignored without affecting thepupil imaging onto the camera.

Ideally, the camera would not need to be focused as the objective systemimaged at different distances. Variables were the RoC and thicknesses ofall the lenses. General parameters were the HeNe wavelength and anon-axis field. A slight field of 0.1 degrees was used for ease ofalignment. Optimization required handholding to bring about the bestsolution. During the optimization, two of the four lenses had minimumeffect on the ray bending, so they were removed, resulting in atwo-element design. Since only one wavelength is required in the pupilimaging module, only one type of glass is required to make the modulework. All of the glasses for the lenses 132, 134 were changed to silicafor ease of manufacturing, and then re-optimized with only slightdegradation in performance. Being in imaging space after interferencehas taken place; this pupil imaging module does not require exceptionaloptical performance. The resulting performance of the pupil imagingsystem with camera was a worst-case WFE of 0.036λ. RMS at the pupilimage on axis for HeNe wavelength.

The resulting pupil imaging system is shown in FIG. 8 with first lens800 and second lens 810. Overall track length of the pupil imagingsystem is 51 mm from relay focus point to the pupil image. The derivedrequirement was 53 mm to maintain the overall apparatus length. Duringdesign the location of the pupil focus varied at best optimization by1.6 mm. To maintain best focus of the interferogram, the camera shouldbe adjustable. A manual focus adjustment with ±6 mm will allow forplenty of margin and to correct for alignment errors.

The below table shows requirements for an exemplary embodiment of apupil imaging module used as part of the present invention (such aselement 130 shown in FIG. 1). While the table shows variousrequirements, the stated requirements apply in the strictest sense onlyto the example given. One skilled in the art would comprehend that otherpupil imaging systems could be utilized in different embodiments of thepresent invention, and that these other pupil imaging modules wouldutilize at least some varied requirements along with perhaps some of therequirements listed in the below table.

Pupil Imaging System Requirements for an Embodiment of the PresentInvention Verification Method Requirement Requirement Units Design UnitsOptical System [Alignment Telescope & Interferometer] Near Focus inFront of Objective Lens 406.4 mm 400 mm Far Focus in Front of ObjectiveLens infinity NA Infinity NA Clear Aperture at Objective Lens ≧35 mm 35mm No Ghosting the Interferes with the Yes NA x System's PerformanceAlignment Telescope WFE (single pass from object to eyepiece λ/3 RMS (λ= all wavelengths) nm 0.12 waves over field) F/# (through focusingrange) 5-8 NA 7 NA Path 1: Object to Eyepiece Yes NA yes NA Path 2:Projected Reticle to Retro Surface Yes NA yes NA to Eyepiece SpectralBandwidth 500-650 nm 486-656 nm Adapter for Color Filter Yes NA x FullField of View ≧1 Degree 1 degrees Null <5 arc seconds Interferometer WFE(reference to test path) ≦λ/5 PV (λ = 633 nm) nm 0.05 waves SpectralBandwidth 633 nm 633 nm Path 1: Source to Reference Retro Yes NA yes NASphere to Camera Path 2: Source to Retro Surface to Yes NA yes NA CameraFringe Visibility for 4 - 100% Reflection 0.25 NA x Full Field of View0.001 Degree 0.001 degrees

For the eyepiece, for example the eyepiece shown in FIG. 1 as element120, no design was created since there are multitudes of commercial offthe shelf versions available.

The performance of an embodiment of the present invention including thealignment telescope portion was determined over all wavelengths andfields for single and/or (depending on operation) double pass models,including evaluation of at least: 1) the Strehl Ratio through system; 2)imaging performance (Polychromatic Strehl), OPD and spot diagram; 3) arcminute resolution over ±30 arc minutes; and 4) arc second resolutionover 10 arc seconds.

WFE was determined by evaluating either the Strehl ratio or the RMS WFEover the entire field for both single and double pass models. Singlepass was used to determine the optical performance when viewing anobject directly as when establishing bore sight. The resulting singlepass WFE performance is shown in FIG. 7. As shown in the figure, RMSwavefront error (WFE) is compared to a varying field. That is,performance is plotted over an entire field consisting of one degree. Atthe very edge of the one-degree field, performance is slightly degraded.However, there is no color separation, so the image would only appearslightly dimmer to the human eye. The human eye would automaticallyaccommodate this loss in signal and fill in the image resulting in goodperformance as viewed over the entire field.

A double pass model was used to determine the performance when theprojected reticle 70 (shown in FIG. 1) was sent out, retro reflected andreturned through the optical system. The model analysis was differentthan with the single pass. In this case, the projected reticle 70 ison-axis with a radius of 4.3 mm. An external flat minor was tilted aboutthe measurement range of 30 arc minutes to determine the performance.The effect was that the center dot of the reticle pattern moves to theedge of the 30 arc minute range and the edge to the center. The angularmotion, of 30 arc minutes, is at the mirror, resulting in a 2:1deviation to mirror angle. Since the system is rotationally symmetrical,only one tilt axis was required. To determine the performance, thepolychromatic Strehl was analyzed and then the polychromatic RMS WFE wascalculated. The following calculation for the RMS WFE was used:Strehl=(1−2π²ω²)²

Rearranging the equation to solve for ω(RMS WFE), the equation is

$\omega = \left( \frac{1 - \sqrt{Strehl}}{2\pi^{2}} \right)^{\frac{1}{2}}$

The resulting polychromatic Strehl ratio across a 4.3 mm field includedgood results. Throughout the entire range, the projected dot possessedgood image quality. The dots were made using all of the designedwavelengths. Since there is no color separation the projection reticle70 can be used with color filters without any degradation inperformance. The lateral color over the angular range of 30 arc minutesis well within the airy disk, as one skilled in the art would readilycomprehend. To finish out the WFE performance for the AIT design, theOPD and spot diagrams were evaluated for both single and double pass.

For single pass, each plot has all wavelengths and fields for a specificconfiguration. In tests over a range from 400 nm to infinite (including10,000 nm, 5,000 nm, 1,000 nm, and 500 nm fields), both the spot and OPDshowed that optical performance was good and varied extremely littleover the entire focusing range. Although the system is not diffractionlimited, performance is actually excellent for its intended use as anoptical imager with the eye as the detector.

To determine the size of the projected reticle pattern, and the abilityto visually see 30 arc minutes of motion, a parametric analysis wasperformed. The double pass model was used with the flat mirror beingtilted at one-minute intervals. Displacements at the relay focus wererecorded and evaluated for uniformity and overall distance. Eachone-minute interval resulted in a displacement of 0.175 mm from theprevious one. For a 30 are minute deviation the maximum displacement atthe relay image plane is 5.26 mm. With a standard 10× eyepiece, each1-arc minute and the entire range of 30 arc minutes are easily viewableby the eye.

Nulling of the projected reticle's center spot to the reference reticlecrosshair to ≦5 arc seconds required the AIT system have magnificationsufficient for the eye to distinguish 5 arc seconds of motion. FIG. 6,element 620, shows the null alignment of the reticles. The projectedreticle dot is centered on the reference reticle crosshair.

A parametric study similar to the 30 arc minute analysis was performed.The range of tilt in the flat mirror was 10 arc seconds at 1-arc secondintervals. Each one-second interval resulted in a displacement of 0.0029mm from the previous one, or 1/60 of that established for eachone-minute interval. For a 10 arc minute deviation the maximumdisplacement at the relay image plane is 0.029 mm. With a standard 10×eyepiece, each 1 arc second interval would result in a 0.029 mm motionthat can be distinguishable. But with the requirement of 5 arc seconds,the motion is 0.145 mm, which is easily detectable. In addition, the eyeis excellent at distinguishing spatial uniformity such as the imagecreated by the overlapping of the projected reticle central dot to thereference reticle crosshair. The AIT will be able to null easily towithin 5 arc seconds.

The performance of an embodiment of the present invention including useas an interferometer was determined at the HeNe wavelength with no fieldusing the double pass model, and included at least the followingevaluations: 1) WFE through AIT over focusing range and 2) fringevisibility for coated and uncoated optics. To perform the analysis, thelocation of the interference needs to be established. This locationdetermines the start point of the common path optics, which does notrequire high performance. In the common path, the interferogram is onlybeing relayed to the detector. Both the reference and test laser wavessee the same aberrations, so a typical WFE of ⅓ wave RMS is acceptable.In the alignment interferometer telescope apparatus, the interferencetakes place at least in part at a location that is approximate to thehypotenuse in beam splitter 20 (shown in FIG. 1 and as discussedpreviously). For subsequent review, the hypotenuse is used as the‘image’ location.

WFE through the alignment interferometer telescope apparatus over thefocusing range was analyzed by overlapping the pupil image of the testlaser wave with that of the reference laser wave. (One model was createdwith both the reference and test laser waves, and various embodiments ofthe present invention could do either or both, or additionalcombinations.) Interferograms as waveform error were created over thefocusing range using the reference laser wave, instead of an idealpupil, to interfere with the test laser wave. This technique resulted inactual performance WFE through the interferometer path. The followingresults were achieved.

Interferometer WFE Results for an Embodiment of the Present InventionFocus Range [mm] PV [waves] RMS [waves] Infinity 0.078 0.022 10,0000.083 0.024 5,000 0.097 0.028 1,000 0.165 0.048 500 0.120 0.034 4000.124 0.036 Ref with Ref 0.000 0.000

To determine the RMS value, a rule of thumb to convert PV to RMS wasused.

${RMS} = \frac{PV}{\sqrt{12}}$

This rule of thumb assumes that the surfaces were manufactured usingstandard fabrication techniques with surfaces having mostly low to midspatial frequencies. Analysis based on the above table shows that thealignment interferometer telescope apparatus has good performance overits entire focusing range, and actually exceeds expectations. Most ofthe residual aberration was spherical with some defocus. The sphericalaberration was expected since a spherical mirror was used to match thef/6.5 objective system. As the f-number increases (larger number) theresidual spherical aberration goes as a function of the aperture squaredfor longitudinal and aperture cubed for transverse. Therefore, byincreasing the f-number, and maintaining the same distance to the retrosphere, the aperture decreases and thus the spherical aberrationdecreases. Off-axis aberration is not applicable, since the system isused only on-axis.

The alignment interferometer telescope apparatus is designed for usewith coated and uncoated optics along with reflective metal surfaces.Each one of these surfaces has different reflectance, so the internalretro sphere needs to also have variable reflectance to ensure goodfringe visibility. To accommodate varying reflectance pellicleattenuation filters are to be used. An analysis was performed todetermine the number of attenuation filters and their attenuationvalues. Fringe visibility is defined as

Fringe  Visibility $V = \frac{I_{\max} - I_{\min}}{I_{\max} + I_{\min}}$

When V equals zero, there is no loss in v. A parametric study was runwith incremental reflectance values for both the test and referencepaths. Through experience, a minimum value of 0.95 was used as the upperlimit for the fringe visibility.

FIG. 11 shows the plot of the low-resolution parametric study. As shownin the Figure, the 0.95 limit, illustrated as a doted line, was used todetermine the number of attenuation filters required. Bold lines showthe attenuation filters. Four attenuation filters are required to spanfrom 1.00 to 0.04. To fine-tune their values another parametric analysiswas performed based on the 0.95 limit and the four chosen values.

FIG. 12 shows the results after fine-tuning the attenuation values. Thefour attenuation values chosen are 0.65, 0.26, 0.10 and 0.04. Thesevalues also allow for overlap at their edges. Since it is easier toremove than increase the intensity, the internal reference sphericalmirror has a protected aluminum coating with a reflectance value of0.65. To achieve the other three values, coated pellicle reticles areused with half the values since this is a double pass system and takeinto account that the internal reference spherical mirror has a value of0.65. The pellicle was chosen since it contributes very little WFE inthe alignment interferometer telescope apparatus reference path designand is readily available. Plus, the diameter required is in the order of12 mm, including mounting. Three attenuation filters plus an open holecan be easily mounted inside the alignment interferometer telescopeapparatus on a wheel, as one of skill in the art would comprehend.

A sensitivity analysis was performed on the alignment interferometertelescope apparatus prior to developing an error budget. The purpose wasto explore the interrelationship between the alignment telescope andinterferometer paths, plus the determination of the most sensitiveparameters. A standard set of parameters is seen below, and is based ona unit value of one. This standard set was used for each model to setupsensitivities.

Parameter Value Lens Surface Surface RoC ±1 mm Thickness ±1 mm DecenterX ±1 mm Decenter Y ±1 mm Tilt X ±1 Degrees Tilt Y ±1 DegreesIrregularity ±1 fringes Index ±1 NA Abbe Number ±1% Lens ElementDecenter X ±1 mm Decenter Y ±1 mm Tilt X ±1 Degrees Tilt Y ±1 Degrees

The performance criteria used was RMS WEF. Both alignment telescope andinterferometer models include all configurations but no compensators.Overall their estimated RMS WFE changes were approximately the same;alignment telescope at 33.450 waves and the interferometer at 35.408waves. Sensitive parameters for each model are listed in the followingtable.

Sensitive Parameters Alignment Interfero- Parameter Surface Telescopemeter Element Decenter in X Relay Lens 3 X X Element Decenter in X RelayLens 4 X X Element Decenter in Y Relay Lens 3 X X Element Decenter in YRelay Lens 4 X X RoC IMG Lens 2 surface 1 X RoC Relay Lens 2 Surface 1 XX RoC Relay Lens 3 Surface 1 X X RoC Relay Lens 3 Surface 2 X X RoCRelay Lens 4 Surface 1 X X RoC Relay Lens 4 Surface 2 X X SurfaceDecenter in X Relay Lens 3 Surface 2 X X Surface Decenter in Y RelayLens 3 Surface 2 X X Surface Tilt in X OBJ Lens 2 Surface 1 X ThicknessIMG Lens 1 surface 1 X Thickness Relay Lens 2 Surface 2 X X ThicknessRelay Lens 3 Surface 1 X X Thickness Relay Lens 3 Surface 2 X X

In general, the above table shows that the alignment telescope andinterferometer have mostly the same sensitive parameters. This isreasonable since both share a common optical path except for theinterferometer including the addition of the pupil imaging system 130(shown in FIG. 1). For the interferometer, the sensitivity analysis wasbased on image performance not creating the interferogram, and thenimaging it in the common path optics of the relay 100 and pupil imagingsystem 130. The interferometer is also a double pass design thateffectively doubles the WFE created by the optical system. Therefore, anew set of parameters taking into account just the objective system maybe used for the interferometer's tighter requirements. The alignmenttelescope may be used with the objective system's error budget to obtainthe relay system's error budget. The pupil imaging system 130 utilizedthe interferometer model's parameters.

The error budget is used to determine the manufacturability of theoptical system. The results are error budget values for each optic andsubsystem. These values include the combined effects of fabricating theoptics, mechanical part fabrication, assembly and alignment tolerances,environmental conditions, and reserves. Initially, a standard set ofparameter values were used. These values were adjusted to take advantageof sensitive and non-sensitive parameters. The goal was to have as loosean error budget as possible for each optical component while maintaininga build yield of 90% or better.

Focus compensation was incorporated into the error analysis since thesystem is adjustable using the secondary lens. One hundred Monte Carloruns were used to acquire the statistics. Based on variousinterferometer requirements, typical 90% values require a PV WFE of λ/5(0.2 waves) or better in double pass. Using only the objective systemthe error budget analysis was performed. The technique was an iterativeprocess that began with standard optical/mechanical tolerances as shownin the below table. After each tolerance run, the values were adjustedbased on the 10 worst offenders and rerun.

Starting Error Budget Parameters Parameter Value Lens Surface SurfaceRoC ±3 fringes Thickness ±0.25 mm Decenter X ±0.1 mm DecenterY ±0.1 mmTilt X ±0.016 Degrees Tilt Y ±0.016 Degrees Irregularity ±0.5 fringesIndex ±0.001 NA Abbe Number ±1% Lens Element Decenter X ±0.1 mm DecenterY ±0.1 mm Tilt X ±0.016 Degrees Tilt Y ±0.016 Degrees

The final build yield of 90% or better resulted in a statistical PV WFEof 0.197 waves, meeting the self-imposed requirement of 0.2 waves. Thesevalues were inserted next into the alignment telescope model includingthe relay lens and used to determine the error budget for the relaysystem. The starting point for the relay lenses was the same as with theobjective system. Self-imposed requirements were for the alignmenttelescope to have within a combined error budget of λ/3 RMS WFE (1.155waves PV). After the initial run, the performance was within statedrequirements with residual error for the eyepiece, so no furtheriterations were performed. The statistical performance was 1.131 wavesPV WFE meeting the self-imposed requirement of 1.155 waves PV. Aresidual PV WFE allocated for the eyepiece was 0.024 waves. This is adirect subtraction that is a worst-case scenario since aberrationsusually do not have their peaks in the same location.

With the alignment telescope system completed, the interferometer pupilimaging module was analyzed for its error budget. The pupil system 130is in common path, after the interferogram has been created; thereforeits requirement for overall WFE is 1 wave PV to meet the 90% or bettermanufacturing yield. Using the same error budget and technique asestablished for the objective and relay system, the pupil imaging system130 was analyzed. The initial run of 0.893 waves PV was well below theWFE requirement, so the iteration process was used but with looseningthe tolerances. Only one parameter was loosened at a time so that theeffect on the WFE could be ascertained. After several iterations, theresulting statistical PV WFE of 0.870 waves was achieved. This value issubstantially below the required 1 wave for better than 90% yield. Butafter multiple iterations of loosening up of the tolerances to over 3×their original values, it was determined that the pupil imaging lensesare not sensitive. Mass production values can be applied to its entireerror budget.

Reference spherical mirror error budget was created separately since theonly powered optic is the reference sphere itself. Its error budget wasrun on a separate model with the self-imposed requirement of ⅕ PV. Asexpected, it was insensitive to almost all parameters. A sphericalsurface has no axis and thus tilting and de-centering have no effect.Change in RoC results in a slightly different f-number. The onlysensitive parameter is the surface figures irregularity that shows up asWFE. Only this parameter needs to be maintained. The rest are restrictedby the mechanical mounts travel range.

A ghosting analysis was performed to determine if the optical designwould have unwanted images forming at the focal and pupil surfaces.Ghost images either appear as washed out, non-focusing, returns or assharp images that confuse the operator as to which is the correctreturn. In the interferometer, another issue with ghost images is theoverlap of spurious fringes that interfere with the true fringes givingmisleading or non-readable fringe patterns. Using the alignmenttelescope and interferometer models already created, the ghost analysiswas run. Parameters for the analysis included all surfaces that have aglass to air interface, all configurations, all wavelengths and allfields. The requirements were that the resulting ghost image spot sizebe at least 10 times larger than the nominal and at least 100 timesdimmer.

With all of the surfaces having Anti-Reflective (AR) coatings, themaximum relative ghost intensity would be 0.01%, based on a conservative1.0% AR coating. Ghost analysis shows that none of the ghost reflectionsimage back at the image/pupil surface. All of them fall out of theoptical path resulting in background scatter, or a light noise DCoffset.

To simplify the AIT assembly it is divided into 6 subsystems that aregenerally labeled in FIG. 2: 1) alignment telescope objective system; 2)beam splitters; 3) interferometer reference path; 4) relay system andbeam splitter; 5) pupil imaging system with camera; and 6) eyepiece.Each subsystem is assembled separately then integrated in the order aslaid out above. The tightest tolerance subsystem is the alignmenttelescope objective system. It requires that the optical and mechanicalaxes maintain alignment over the entire focusing range.

The assemble of the alignment telescope objective system is furtherdivided into three stages 1) mounting of the lenses; 2) integrating thelenses into the barrel; and 3) attaching the secondary lens mechanicalcomponents. Each module consists of an air spaced doublet, one for theobjective and secondary.

First the empty cell is aligned on an air bearing table and centered toan optical reference beam. Then the first lens (for example, lens 80 ofFIG. 1) is inserted and centered to the optical axis by rotating thelens and adjusting by translating the lens. After the lens is centeredit is held in place with an elastomer in dots around the circumference.With the lens secured, a spacer is inserted, and the second lens 90 isinstalled using the same technique as the first.

With both the objective and secondary lenses mounted in their cells,they are integrated into a barrel housing (not shown). The barrel ismounted onto the air bearing and aligned to the optical reference beam.After it is aligned the objective lens 80 is inserted. Adjustment screwsposition the lens to the center of the optical axis and then it issecured. With the objective lens 80 secured, the secondary lens 90 isinserted into the barrel. The secondary lens 90 is aligned as theobjective lens 80 over its entire travel range. Once the secondary lens90 is aligned to the optical axis, it is secured in place. To finish outthe objective assembly, mechanical hardware for adjusting the secondarylens 90 is installed.

The integration of the beam splitter 20, 60 assembly into the barrel isnext. By including the beam splitters 20, 60 in the barrel, the opticaland mechanical axes can be maintained. Openings in the barrel allow thedifferent optical paths clear access to the beam splitters 20, 60. Priorto integration into the barrel, the beam splitters 20, 60 and the retrosphere reference spherical mirror 30 are mounted in a subassembly. Thecemented beam splitters 20, 60 are first mounted into the subassemblyand aligned using mechanical tolerances.

Afterwards, the mounted beam splitters 20, 60 are placed in front of anf/18 focusing interferometer, focused onto the beam splitter surface.The centering is determined by mechanical alignment. Integration of thespherical mirror and its attenuation wheel is next onto the subassembly.It is adjusted until its retro beam aligns with the f/18 beam. Fineadjustment is performed to null the fringe pattern. The reticle 70 isthen installed onto the beam splitter surface.

Adjustments are made to the reticle 70 housing until the crosshairpattern is aligned to the microscopes optical axis. This alignment ispreliminary to allow quicker alignment after the subassembly isintegrated into the barrel. The beam splitter 20, 60 assembly isintegrated into the barrel which is still mounted and aligned on the airbearing table. Again the barrel is rotated and the return images fromthe beam splitter 20, 60 are aligned to the optical axis, using beamsplitter subassembly adjusters. Next the reticle 70 crosshair is alignedto the optical axis by focusing onto it with the optical axis system.The reticle 70 and beam splitter 20, 60 subassemblies are fixed in placeand the alignment interferometer telescope assembly continues with thealignment of the reference spherical mirror 30.

Integration of the retro sphere/reference spherical mirror 30 wasperformed with the beam splitters 20, 60 but the mirror was not aligned.To align the reference spherical mirror 30, the optical axis beam isagain focused onto the surface of the reticle. The reference laser wavereturns from the reference spherical mirror 30 and is aligned to it.After it is aligned, it is secured in place or to allow adjustments bythe user, its adjustment actuators locations are set to zero.

Light source 40 is integrated next. An exemplary embodiment of thepresent invention uses a small incandescent bulb with a green filter.The small bulb is designed so that a high intensity light source can beinserted in place of the incandescent bulb. A SMF fiber is attached tothe mounting for the interferometer light source. Adjusting the fiberuntil the return image goes back into the optical axis system that isstill focused and centered on the crosshair reference reticle 70 and theSMF fiber itself performs alignment. The fiber is then locked in place.

With the precision barrel assembly complete, it can be removed from theair bearing and placed on a bench top for final optical integration. Therelay system 100 and beam splitter 20, 60 are assembled separately on abench using mechanical tolerances. The same are then attached to thebarrel. Focus and centering is achieved by viewing the referencecrosshair pattern. A tooling reticle at the location of the eyepiece isused as an alignment aid to align the beam splitter 20, 60. The relaysystem 100 except the beam splitter 20, 60 is now secured in place.

Integration continues with the pupil imaging system 130 and camera 140.Like the relay system 100, the pupil imaging system 130 and camera 140are aligned using mechanical tolerances. Pupil focus is verified byturning on the HeNe laser, then placing an optical flat in front of thealignment interferometer telescope, and aligning the interferometer pathwith several fringes as one of skill in the art would comprehend. Theresulting interferogram is imaged onto the camera 140. Focus andmagnification is adjusted by moving the camera 140 and/or the pupilimaging 130 optics system.

In order to be able to attach the eyepiece and perform final alignmentto the pupil imaging system 130, the back housing is installed (notshown). It is designed to be integrated from the back end of the barrel.Therefore, in an exemplary embodiment of the present invention, all ofthe pre-mentioned subassemblies are required to be smaller in diameterthan the barrel, except for the reference spherical mirror 30. A cutoutin the housing may allow the housing to slip around the referencespherical mirror 30. This cutout gives the user accessibility toadjustment screws at the reference spherical mirror. A side lid with ametal cover allows access for all of the following integrations andalignments and protects the internal optics.

Next, the secondary lens 90 adjustment knob mechanical linkage isintegrated and tested. All of the fiber and electrical connections areattached to the housing. Integration of the eyepiece 120 and finalalignment is performed. The housing has a fixed threaded hole for theeyepiece to attach to. Alignment of the beam to the eyepiece is done viathe relay optical system beam splitter 110. Adjustments are made toalign the crosshair reference reticle 70 to the center of the eyepiece.After the eyepiece is adjusted, the pupil imaging system 130 is adjustedto adjust for any translations due to beam splitter 20, 60 motions. Thenthe relay system beam splitter 20, 60 and pupil imaging system 130 andcamera 140 are fixed in place.

Final assembly verification is performed by testing the alignmentinterferometer telescope apparatus on a series of predetermined targetsand retro reflectors at specific distances. The barrel is rolled insideof a mounting fixture to test that the optical and mechanical axes meetrequirements. Following the previous, the alignment interferometertelescope apparatus is ready for use.

Exemplary embodiments of the present invention were tested in variousfashions including the following. All of the optics and mounts werecollected and assembled on a 4×8 foot optical table. The lenses weremounted in Newport mounts. On the sides of each lens mount, the lenspart number was recorded along with the lenses orientations. Analignment telescope (D275) was used to align the lenses onto a Newportsliding rail system.

To align the optics to a central gut ray, an iris was positioned atclose and far locations on the slide. The alignment telescope wasaligned to the irises using the 50/50 technique. At the close location,translation was used, and at the far location, angle was used. After afew iterations the alignment telescope was aligned to the slide. Alayout of the previous is shown in FIG. 3, where the objective lens islocated to the left of the illustration, a test laser wave path 320 anda reference laser wave path 370 travel along two different axis and meetin perpendicular fashion, the beam splitter 330 sits at the juncture ofthe two laser wave paths 320, 370, the secondary lens rests to the leftof the beam splitter 330, the reference spherical mirror 350 sits behindthe beam splitter in reference to the interferogram 380, and the lasersource 360 is located generally to the right of all the previous and isproviding a laser wave to the beam splitter 330.

In assembling the components shown in FIG. 3, the secondary lens 340 wasattached to the rail and aligned first. Retro reflections from the lens340 were used to align it in tip/tilt and XY de-center. A slide test wasperformed to verify error in alignment over the secondary travel range.Angular error of less than 1 arc minute and de-center error less than0.1 mm was observed. These misalignments changed the WFE in the model byless than 0.005 PV, which is undetectable by the human eye. Next theobjective lens 310 was aligned using the same technique. Afterwards bothof these lenses 310, 340 were removed and the rail was laid out with thepositions for each optic based on the infinity object opticalprescription. First the secondary lens 340 was positioned onto the railto allow room for all of the other optics and their mounting. Then thebeam splitter 330 was located at 35 mm away from the secondary lens 340using a steel ruler. A SMF was connected to the HeNe laser generator andthe other end positioned 25 mm behind the beam splitter 330. Optimumlocation of the objective lens 310 was determined by looking at theoutput beam with a shear plate. Once the location was found for infinityfocus, the objective lens 310 was locked down and the location of thesecondary lens 340 marked.

FIG. 4 shows exemplary components used for focus adjustment. Focusadjustment is performed by moving the secondary lens 330 between thebeam splitter 340 and objective lens 310. For infinity focus thesecondary lens 330 is positioned close to the beam splitter 340 and atnear focus it is positioned towards the objective lens 310. A visualtest of the lab setup being used as an alignment telescope was performedwith the laser generator turned off.

Referring to FIG. 1, illuminated objects were viewed through an eyepiece120 by being held where the interferogram is projected out of the beamsplitter 20, 60. Different secondary mirror positions were used to viewobjects from 500 mm to infinity that were placed around the lab in astraight line. Each object could be focused onto and was viewed with nodiscernable aberrations.

To test the interferometer portion of the AIT, the laser generator wasturned on and a flat mirror was positioned in front of the objectivelens. It was adjusted in tip and tilt until the laser beam return spotwas aligned to the outgoing laser beam emanating from the SMF fiber.This was easy to visually align since the holder for the SMF fiber has alarge mounting surface, as seen in FIG. 5. The retro image was viewablewith the unaided eye, as noted by element 510 in FIG. 5.

With the test path aligned, the built in reference spherical mirror 30(as shown in FIG. 1) was adjusted for alignment using the same process.The mirror 30 was adjusted using translation to return its retro imageonto the same spot on the SMF fiber 500 (shown in FIG. 5). In additionto position, it was also aligned in piston. To correct piston theinterference pattern was viewed as shown in FIG. 13. Alignment wascorrect when the null fringe was achieved. The interference pattern wasclean and easily viewable with the unaided eye, with vertical fringesshown as element 1300, null fringes shown as element 1310, andhorizontal fringes shown as element 1320. Note that the straight fringesshow a bump at the center and the null has 1 fringe of residual error.This spherical aberration is predicted. To determine the amount ofspherical aberration, we use the following equation.

${FE} = {{\frac{\lambda}{2}\frac{\Delta}{S}} = {{\frac{0.6328\mspace{14mu}{µm}}{2}\frac{7}{8}} = {0.277\mspace{14mu}{µm}\;{PV}}}}$

The amount of spherical aberration calculated from in the optical modelis therefore:SA=0.2739λ=0.173 μmPV

The difference between the predicted and the test is due to the additionof the error stemming from the internal reference spherical mirror 30(FIG. 1).

A test was performed to verify that the secondary lens could be used toset the focus for retro returns off of spherical surfaces. Approximately740 mm in front of the objective lens, a concave interferometer retrosphere was inserted into the beam path. This secondary mirror wasadjusted in position towards the objective lens for best focus of theretro image at the SMF fiber. Afterwards the retro dot was aligned tothe reference spherical mirror's (FIG. 1, element 30's) dot. Adjustmentof the retro dot may be performed by translating the concaveinterferometer retro sphere, and not the internal retro sphere. Notethat with a spherical surface there is no defined axis; thereforetranslation and tip/tilt are the same in terms of adjustments. The onlyconcern is vignetting of the beam. With the two dots overlapped theinterferogram image was evaluated. This process is the standard two-dotalignment technique that is used on many interferometers.

At this point, circular fringes were visible, such as those shown inFIG. 14. Circular fringes signify that the test path is not at the bestfocus. All adjustments were performed using a Zygo mount. The alignmentinterferometer telescope apparatus's retro sphere was not adjusted sincedoing so would induce errors in the reference path and take the systemout of infinity focus. By adjusting the Zygo mount the fringes werefeathered out till three to five fringes were visible. This number offringes is easy for the eye to see and deduce the WFE. The residualspherical aberration is visible at best focus. Element 1400 shows 7fringes out of focus, element 1410 shows 5 fringes out of focus, andelement 1420 shows a preferred focus.

Another test was performed that retro reflected the focus spot off of aflat mirror. In this configuration, the rays are flipped after beingreflected, as illustrated in FIG. 15. The top becomes the bottom andvise versa. To setup the test, the mirror was positioned 1 meter infront of the objective lens. Using the secondary mirror, the focus wasimaged onto the mirror. Mirror adjustments were used to align the retrobeam with the reference beam dot. The fringe pattern showed that the WFEhad decreased. This was expected since the rays are reversed resultingin a cancellation of the errors. Element 1520 of FIG. 15 shows a retromirror with laser spot, element 1500 shows vertical fringes, and element1510 shows horizontal fringes.

The previous lab test of the alignment interferometer telescopeapparatus shows that the instrument works as both an alignment telescopeand an interferometer, and that the operational concept is correct.

Additional aspects of embodiments of the present invention may includethe following, whether taken individually, in part, or collectively. Oneaspect includes an adaptor that slips over the end of the housing barrelas an aid in alignment and to set a visible line of sight. The adaptormay consist of a visible laser diode that projects a collimated pencilbeam that is close to the alignment of the optical axis. Batteries builtinto the adaptor supply power. For aligning mirror systems, the retroreturn beam may adjust to overlap the outgoing beam. The adaptor is thenremoved and the mirror's retro return would be visible in the alignmentinterferometer telescope apparatus. The beam gives a visiblerepresentation of the alignment interferometer telescope apparatus'soptical axis for aid in aligning objects at great distances.

For interferometer aspects, three additional concepts are presented.First, by using a laser diode, the bulky, external HeNe laser andassociated fiber delivery system and power supply may be eliminated. Thelaser diode may be mounted inside the alignment interferometer telescopeapparatus's housing along with drive electronics. A mounting compartmenton the side of the MT allows user access. This access provides forchanging of the laser diode wavelength by inserting a separate laserdiode module.

An insertable notch filter may also be used at the eyepiece to eliminatelaser damage to the eye. The notch beam splitter may be replaced with a50/50 style. Further, a short coherence length laser may be used toeliminate spurious fringe patterns from the optics under test and thebeam splitter cemented interfaces. This also allows greater flexibilityin laser diode selection since odd wavelength devices have shortcoherence lengths. Using such lasers may require a delay line forinterference in the reference path.

To accommodate a required path length, a collimating system with a smalldiameter beam may be used to allow it to fit in the AIT body. A multiplefold system with squiggle motor actuators may adjust the delay line. Todetermine the correct delay line path length, a pop in focusing lens maybe used. The operational concept would be to adjust the fringes untilnull fringe is achieved. For longer path lengths, plug in fiber delaylines may be attached to the side of the alignment interferometertelescope apparatus. Additionally, spatial carrier frequency phaseshifting software could be incorporated to accurately measure the opticunder test performance. The manual adjustments on the referencespherical mirror may be used to induce approximately one wave per fourpixels on the camera. Using just one camera frame capture, the wavefrontincluding phase can be accurately calculated and displayed.

The design, assembly, and operational usage of the alignmentinterferometer telescope apparatus has been demonstrated and analyzed.Based on the previous the alignment interferometer telescope apparatushas been shown to function as described above. Further, each of thefollowing self-imposed requirements has been addressed and is met orexceeded. The below table shows self-imposed requirements for anexemplary embodiment of the present invention (such as those elementsshown in FIG. 1). While the table shows various requirements, the statedrequirements apply in the strictest sense only to an exemplaryembodiment of the invention. One skilled in the art would comprehendthat other embodiments could be utilized to practice the presentinvention, and that the other embodiments would utilize at least somevaried requirements along with perhaps some of the requirements listedin the below table.

Verification Method Requirement Requirement Units Design Units OpticalSystem [Alignment Telescope & Interferometer] Near Focus in Front ofObjective Lens 406.4 mm 400 mm Far Focus in Front of Objective Lensinfinity NA Infinity NA Clear Aperture at Objective Lens ≧35 mm 35 mm NoGhosting the Interferes with the Yes NA Yes NA System's PerformanceAlignment Telescope WFE (single pass from object to eyepiece λ/3 RMS (λ= all wavelengths) nm 0.12 waves over field) F/# (through focusingrange) 18-23 NA 7 NA Path 1: Object to Eyepiece Yes NA Yes NA Path 2:Projected Reticle to Retro Surface Yes NA Yes NA to Eyepiece SpectralBandwidth 500-650 nm 486-656 nm Adapter for Color Filter Yes NA Yes NAFull Field of View ≧1 Degree 1 degree Null <5 arc seconds <5 acr secondsInterferometer WFE (reference to test path) ≦λ/5 PV (λ = 633 nm) nm 0.05waves Spectral Bandwidth 633 nm 633 nm Path 1: Source to Reference RetroYes NA Yes NA Sphere to Camera Path 2: Source to Retro Surface to Yes NAYes NA Camera Fringe Visibility for 4 - 100% Reflection 0.25 NA <0.25 NAFull Field of View 0.001 Degree 0.001 degree General Interferometer NullFringe On-Axis NA Yes NA Polarization NA NA NA NA Camera Adapter forEyepiece Yes NA Yes NA Interferometer 2 Dot Alignment via Yes NA Yes NAAlignment Telescope Alignment Overall Length ≦650 mm 580 mm BarrelLength ≦360 mm 330 mm Barrel Diameter 2.24966 ± 0.00025 inches 2.24966 ±0.00025 inches Optical Axis Concentric with Barrel (at 16 ±0.0003 inches±0.0003 inches inches) Camera for Interferometer Yes NA Yes NA HousingMaterial Metal NA Metal NA Lens & Beamsplitter Material Glass NA GlassNA

As described above, it is possible to implement some aspects of thepresent invention as a method and/or in a computer system. The computersystem may include a bus or other communication mechanism forcommunicating information, and a processor coupled with the bus forprocessing information. The computer system may also include a memorycoupled to the bus for storing information and instructions to beexecuted by the processor. The memory may also be used for storingtemporary variables or other intermediate information during executionof instructions by the processor. The computer system further may alsoinclude a data storage device, such as a magnetic disk or optical disk,coupled to the bus for storing information and instructions. Thecomputer system may be coupled to a display device for displayinginformation to a user. An input device, such as, for example, a keyboardor a mouse may also be coupled to the computer system for communicatinginformation and command selections to the processor.

According to some embodiments of the present invention, selectiveadjustment of a pupil image and/or a reticle may be performed utilizingsoftware, an algorithm, a processor, and/or a computer system inresponse to an output of a processor executing one or more sequences ofone or more instructions contained in a memory. Such instructions may beread into the memory from a machine-readable medium, such as a datastorage device.

A Masters of Science thesis by Paul F. Schweiger, entitled Design of anAlignment Telescope with a Built-In Interferometer, University ofArizona College, Optical Sciences Program, 2007, is hereby incorporatedby reference in its entirety for all purposes. The description of theinvention is provided to enable any person skilled in the art topractice the various embodiments described herein. While the presentinvention has been particularly described with reference to the variousfigures and embodiments, it should be understood that these are forillustration purposes only and should not be taken as limiting the scopeof the invention.

There may be many other ways to implement the invention. Variousfunctions and elements described herein may be partitioned differentlyfrom those shown without departing from the spirit and scope of theinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and generic principles definedherein may be applied to other embodiments. Thus, many changes andmodifications may be made to the invention, by one having ordinary skillin the art, without departing from the spirit and scope of theinvention.

It is understood that the specific order or hierarchy or steps in theprocesses disclosed herein is an illustration of exemplary approaches.Based upon design preferences, it is understood that the specific orderor hierarchy of steps in the process may be re-arranged. Some of thesteps may be performed simultaneously. The accompanying method claimspresent elements of the various in a sample order and are not meant tobe limited to the specific order or hierarchy presented.

A reference to an element in the singular is not intended to mean “oneand only one” unless specifically stated, but rather “one or more.” Theterm “information” derived from a radio frequency signal may includedata (e.g., audio, video, multimedia, instructions, commands, or otherinformation). The term “some” refers to one or more. Underlined and/oritalicized headings and subheadings are used for convenience only, donot limit the invention, and are not referred to in connection with theinterpretation of the description of the invention. All structural andfunctional equivalents to the elements of the various embodiments of theinvention described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and intended to be encompassed by theinvention. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the above description.

1. A method for a telescope, the method comprising: producing a coherentlaser wave; splitting the coherent laser wave into a reference pathlaser wave and into a test path laser wave; transmitting the test pathlaser wave to an object outside the telescope; receiving the test pathlaser wave at an interference location within the telescope uponreflection from the object; reflecting the reference path laser wave tothe interference location; combining the reference path laser wave andthe test path laser wave to produce a combined laser wave; producing alight; projecting an image from a first reticle with the light;transmitting the projected image to the object; receiving the projectedimage at a second reticle; and superimposing the projected image with areference image from the second reticle.
 2. The method of claim 1,further comprising: producing a first pupil image for the reference pathlaser wave, the first pupil image being based on the combined laser waveand the reference path laser wave; and producing a second pupil imagefor the test path laser wave, the second pupil image being based on thecombined laser wave and the test path laser wave.
 3. The method of claim1, further comprising selectively adjusting at least one of the firstreticle and the second reticle to align the telescope.
 4. The method ofclaim 1, further comprising selectively adjusting at least one of thefirst pupil image and the second pupil image to align the telescope. 5.The method of claim 1, further comprising selectively adjusting at leastone of the first reticle and the second reticle and at least one of thefirst pupil image and the second pupil image, to align the telescope. 6.The method of claim 2, further comprising imaging the first pupil imageand the second pupil image at a viewing plane.